Strength measures bodily power, athletic training, and the extent to which you can exert raw physical force.

Strength Checks

A Strength check can model any attempt to lift, push, pull, or break something, to force your body through a space, or to otherwise apply brute force to a situation. The Athletics skill reflects aptitude in certain kinds of Strength checks.
Athletics. Your Strength (Athletics) check covers difficult situations you encounter while climbing, jumping, or swimming. Examples include the following activities:

Other Strength Checks. The GM might also call for a Strength check when you try to accomplish tasks like the following:

Attack Rolls and Damage

You add your Strength modifier to your attack roll and your damage roll when attacking with a melee weapon such as a mace, a battleaxe, or a javelin. You use melee weapons to make melee attacks in hand-to-hand combat, and some of them can be thrown to make a ranged attack.

Lifting and Carrying

Your Strength score determines the amount of weight you can bear. The following terms define what you can lift or carry.
Carrying Capacity. Your carrying capacity is your Strength score multiplied by 15. This is the weight (in pounds) that you can carry, which is high enough that most characters don't usually have to worry about it.
Push, Drag, or Lift. You can push, drag, or lift a weight in pounds up to twice your carrying capacity (or 30 times your Strength score). While pushing or dragging weight in excess of your carrying capacity, your speed drops to 5 feet.
Size and Strength. Larger creatures can bear more weight, whereas Tiny creatures can carry less. For each size category above Medium, double the creature's carrying capacity and the amount it can push, drag, or lift. For a Tiny creature, halve these weights.

Variant: Encumbrance

The rules for lifting and carrying are intentionally simple. Here is a variant if you are looking for more detailed rules for determining how a character is hindered by the weight of equipment. When you use this variant, ignore the Strength column of the Armor table.
If you carry weight in excess of 5 times your Strength score, you are encumbered, which means your speed drops by 10 feet.
If you carry weight in excess of 10 times your Strength score, up to your maximum carrying capacity, you are instead heavily encumbered, which means your speed drops by 20 feet and you have disadvantage on ability checks, attack rolls, and saving throws that use Strength, Dexterity, or Constitution.